Synthesis, characterization and DNA-binding of novel chiral complexes Δ- and Λ-[Ru(bpy)2L]2+ (L = o-mopip and p-mopip)

Novel chiral Ru(II) complexes [Ru(bpy)2L]2+(bpy = 2,2-bipyridine; L: o-mopip = 2-(2-methoxylphenyl)imidazo[4,5-f][1,10]phenanthroline, p-mopip = 2-(4-methoxylphenyl)imidazo[4,5-f][1,10]phenanthroline) containing –OCH3 at different positions on the phenyl ring have been synthesized and characterized. The DNA-binding and DNA-photocleavage properties of the complexes were investigated. The theoretical calculations for these complexes were also carried out applying the density functional theory (DFT) method. The experimental results show that: both these two isomer complexes can bind to DNA in an intercalative mode; the DNA-binding affinity of [Ru(bpy)2(p-mopip)] 2 is greater than that of [Ru(bpy)2(o-mopip)] 1; moreover, the DNA-binding affinities of enantiomers Δ-1 and Δ-2 are all greater than those of Λ-1 and Λ-2, respectively. In addition, a very interesting finding is experimentally obtained, i.e. under a low [DNA]/[Ru] ratio, the emission intensities of Δ-1 and Λ-1 are all weaker than those of Δ-2 and Λ-2, however, upon a high [DNA]/[Ru] ratio, the emission intensities of both Δ-1 and Λ-1 are stronger than those of Δ-2 and Λ-2. Such a difference of the emission spectra can be interpreted by the electric effect of substituent on the intercalative ligand. The difference in DNA-binding affinities of these two isomeric complexes can also be reasonably explained by the DFT calculations.